Cord Reel Variable Current Thermal Management and Damage Detection

ABSTRACT

A battery charging assembly includes a load management system, a charging cord with a battery connector, and circuitry for detecting cord removal or damage. The load management system monitors the heat buildup in a coiled portion of the charging cord and issues a corresponding signal to control the current flowing through the cord.

This application is a continuation of prior application Ser. No.14/997,884 which is a continuation of application Ser. No. 13/968,268,now U.S. Pat. No. 9,238,416, The Applicant hereby incorporates byreference application Ser. Nos. 14/997,884 and 13/968,268, now U.S. Pat.No. 9,238,416 in their entireties.

FIELD OF THE INVENTION

The present invention relates generally to management of the generationof heat in a retractable cord reel apparatus delivering electricalpower, and more specifically to insuring that the flow of electricalcurrent in a cord which may be partially or fully coiled on a reel doesnot result in generation of excessive heat which could damage the cord,reduce its useful life, or create danger to the user. Cords used forcharging batteries in, for example, electric vehicles, are frequentlycoiled when not in use to safely store the cord and protect it from theelements and damage.

A retractable cord reel may be part of a charging station in, forexample, a parking lot at an airport or in a home or office garage. Thecharging station may be a post or other suitable structure containingthe cord reel and associated circuitry. If used in a public location,storing the cord on a reel helps protect against theft of the cord forits copper, because the charging station can require use of a key cardor similar means to allow use of the station.

The cord may be only partially unreeled when used to charge a battery.Heat generated by the flow of current will not escape as readily from acord carrying electrical current when the cord is partially orcompletely coiled. As the amount of cord on the reel increases, moreheat tends to be trapped. Overheating could occur even if the cord issimply looped over a hook, rather than being stored on a rotating reel.

The cord reel assembly described here includes improved features forlimiting the current flow in the cord, with higher currents beingpermitted if the cord is substantially or fully unreeled, and forsensing the temperature of the reeled cord at one or more locations.Current flow therefore need not be limited to an unnecessarily low valuesuitable for a cord that is fully coiled. Higher currents, and thereforeshorter charging times, are made possible.

BACKGROUND OF THE INVENTION

Retractable cord reels have been used in various applications toretractably store various types of cables. Typically, a reel might havea stationary end and a retractable end, the retractable end capable ofextension from and retraction back into the reel, and which can beconnected to, for example, a battery in an electric vehicle. Using areel provides convenient storage for the cord. The reel also protectsthe cord from damage, since it need not be left on the ground. Damage tothe cord is reduced. The hazard presented to a user by a damagedelectrical cord is also avoided.

The use of a reel has a disadvantage, because the flow of currentgenerates heat in the cord. A larger current tends to generate moreheat. One application is a charging station for an electric vehicle. Ifthe user parks his electric vehicle very close to the charging station,or if the vehicle is small, it may not be necessary to unreel more thana short length of cord sufficient to reach the battery connector on thevehicle. As current flows from the charging station to the vehicle, heatwill be generated in the cord. Because most of the cord is coiled on thereel, heat cannot escape as readily, and the cord temperature can rise,possibly to the point where the function of the charging station, or thesafety of the user, is jeopardized. An additional factor is the lack ofexperience or knowledge on the part of many vehicle operators.

DEFINITION OF TERMS

The following terms are used in the claims of the patent as filed andare intended to have their broadest plain and ordinary meaningconsistent with the requirements of the law:

A “retractable cord reel” refers to a cable storage unit and cablemanagement systems having a spooling cord such as the type found in U.S.Pat. No. 5,094,396 to Burke, the subject matter of which is herebyincorporated by reference, and U.S. Patent Application No. 2007/0262185to Burke, the subject matter of which is also hereby incorporated byreference.

An electric vehicle means any vehicle, including one propelled solely bya rechargeable battery, and one using hybrid propulsion including arechargeable battery.

Where alternative meanings are possible, the broadest meaning isintended. All words used in the claims set forth below are intended foruse in the normal, customary usage of grammar and the English language.

SUMMARY OF THE INVENTION

The present invention relates to one or more of the following features,elements or combinations thereof.

One disclosed embodiment is directed to improvements in a retractablecord reel for battery charging stations, including those used forvehicles propelled at least in part by rechargeable batteries. Thecharging station includes an electric cord connected to a source ofpower. An end of the cord has a vehicle connector assembly. Controlcircuitry regulates the current supplied to the battery being charged.The reel has one or more temperature sensors for determining the thermalbuildup in the cord. The control circuitry includes a processor thatreceives an input signal from one or more of the sensors. The processorissues an output signal that is related to the input signal from thesensor or sensors. The output signal limits the charging current beingsupplied to the battery, so that the cord does not overheat. Heatgenerated in the cord is safely dissipated.

In another embodiment, the disclosed apparatus includes a sensor fordetermining the amount of cord that has been unreeled. As the length ofunreeled cord increases, the processor receives an input signalrepresentative of the length of unreeled cord, and issues an outputsignal increasing the maximum allowable current to the battery beingcharged.

Thus, it can be seen that one object of the disclosed invention is toprovide a mechanism for the avoidance of overheating a battery chargingstation, and in particular the charging cord.

A further object of the present invention is to allow the maximumcharging current to be delivered to the battery being charged.

Another object of the invention is to detect damage to the cord, orremoval of the cord.

It should be noted that not every embodiment of the claimed inventionwill accomplish each of the objects of the invention set forth above.For instance, certain claimed embodiments of the invention will notrequire a temperature sensing device. In addition, further objects ofthe invention will become apparent based upon the summary of theinvention, the detailed description of preferred embodiments, and asillustrated in the accompanying drawings. Such objects, features, andadvantages of the present invention will become more apparent in lightof the following detailed description of a best mode embodiment thereof,and as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a charging station with a cord reel cordreel assembly according to one embodiment of the present invention;

FIG. 2 is a block diagram of a board assembly used with one embodimentof the present invention.

FIG. 3 is a block diagram of a cord damage or removal detector.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

As can be seen in FIG. 1, a charging system 10 includes an alternatingcurrent (AC), 120 volt power input 12. AC power is connected to a relay14, which in this case is a double-pole, single throw switch that makesor breaks connections between power input 12 and a vehicle connector 16.Those of skill will understand that the relay can include connection foreither or both of AC-Line and AC_Neutral and/or LINE2 (for the case of aLevel 2 charger). In this embodiment, because the battery is used forpropulsion in a vehicle, vehicle connector 16 is constructed inaccordance with SAE Surface Vehicle Recommended Practice J1772, “SAEElectric Vehicle Conductive Charge Coupler,” issued by the Society ofAutomotive Engineers for electric vehicles. For different applicationsnot involving an electric vehicle, connector 16 need not comply withJ1772, and its design can be modified as required by the intended use.

Connector 16 includes electrical connections for ground 18, AC line 20,AC neutral 22 and pilot signal 24. A current transformer 28 is used forground fault interruption to protect a user from injury. Relay 14, pilotsignal 24, and current transformer 28 are connected to board assembly26. Board assembly 26 controls whether relay 14 is open or closed. TheAC connect input between relay 14 and a microcontroller 38 on boardassembly 26 may signal microcontroller 38 whether relay 14 is open orclosed.

When used for charging an electric vehicle, the preferred embodiment ofthe system described herein is a Level 1 charger, as that functionalityis described by the California Air Resources Board and codified in title13 of the California Code of Regulations, the U.S. 1999 NationalElectrical Code section 625 and in SAE International standards. Suchsystems use lower voltage and are therefore less expensive and suitablefor use at a home or other locations where 120 volt AC power is readilyavailable. Due to the relatively low voltage, charging times are longer,possibly as much as ten to twelve hours for a full recharge of anelectric vehicle battery. However, those of skill will understand thatthe present invention as defined by the claims covers not only Level 1chargers, but also chargers designated as (for instance) Level 2 underthose same standards.

The pilot signal for an electric vehicle application according to SAEstandard J1772 is a square wave signal with a frequency of onekilohertz. It varies in amplitude between plus and minus 12 volts. A 12volt power supply 30 provides a reference voltage for the pilot signal24. Power supply 30 also provides power for microcontroller 38 on boardassembly 26. The pilot signal 24 communicates between the vehicle andthe board assembly 26. Pilot signal 24 controls the amount of currentdelivered to the vehicle battery being charged. The amount of current isvaried by altering the duty cycle of the square wave, that is, the pulseduration divided by the pulse period. A lookup table stored in theelectric vehicle contains the variation in the duty cycle necessary fora given current, though those of skill will understand that the dutycycle could alternatively be generated by an algorithm “on the fly” byusing the teaching of the present invention. For example, a duty cycleof 26.7% correlates to a current of 16 amperes under the J1772 standard.

The duty cycle is also varied in the present embodiment according to theamount of cord that is unreeled. The amount may be determined directlyor indirectly. For example, a potentiometer can be used, which willindicate how much of the cord is unreeled, and therefore indirectlyindicate the amount of heat that will be generated in the reeled portionof the cord. (Not clear to me how the pot indicates the amount ofunreeled cord.) A direct measurement of heat generation in the reeledcord can be determined by a thermistor, a thermocouple, or digitaltemperature sensor installed in the cord reel as shown in FIG. 2. Third,the current transformer 28 and a sensor of reel rotation may be employedwith a lookup table stored in the microcontroller identifying themaximum current for a given length of unreeled cord.

Regardless of the type of sensor, the sensor signal is delivered toboard assembly 26, as shown in FIG. 2. In this embodiment, boardassembly 26 includes an AC relay control 32 that controls relay 14. Apilot driver 34 is on board assembly 26. Driver 34 modulates the pilotsignal duty cycle to control the amount of current flowing through thecord to the vehicle battery. A pilot level shifter 36 can receive asignal from the car to confirm or determine, for instance, the currentrequired to bring the car battery to a full charge. Temperature sensorinput 42 receives a signal from a potentiometer, thermistor or digitaltemperature sensor as shown in FIG. 2. Ground fault detection circuit 44receives an input from current transformer 28. Detection of a faultcauses microcontroller 38 to open relay 14, shutting off current.

Relay control 32, driver 34, shifter 36, sensor input 42, and detectioncircuit 44 are connected to microcontroller 38 which can be programmedby one of skill in the art. One suitable microcontroller is an AtmelATMEGA328P from Atmel Corporation of San Jose, Calif.

While the disclosure is susceptible to various modifications andalternative forms, specific exemplary embodiments thereof have beenshown by way of example in the drawings and have herein been describedin detail. It should be understood, however, that there is no intent tolimit the disclosure to the particular embodiments disclosed, but on thecontrary, the intention is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of the disclosure asdefined by the appended claims.

What is claimed is:
 1. A vehicle charging system (10) including a loadmanagement mechanism for providing a limitation on the current suppliedto an electric vehicle, the system comprising: a) An electric cord andvehicle connector assembly (16); b) A pilot signal provided via theelectric cord and vehicle connector assembly (24) for regulating thecurrent supplied to the electric vehicle; c) A sensor for determiningthe thermal buildup in the electric cord and vehicle connector assembly(42); and d) A processor (38) located on the vehicle charging system forreceiving an input from the sensor correlating to the thermal buildup inthe electric cord and vehicle connector assembly, the processormodifying the pilot signal based upon such input so as to limit thelevel of current being supplied to the electric vehicle.
 2. The vehiclecharging system of claim 1 wherein the electric cord and vehicleconnector assembly comprises a retractable cord reel including a spoolfor retracting and extending an electrical cord for supplying a chargeto an electric vehicle.
 3. The vehicle charging system of claim 2wherein the sensor for determining the thermal buildup in the electriccord and vehicle connector assembly comprises a sensor for determiningthe extent to which the retractable cord reel has been extracted fromthe spool.
 4. The vehicle charging system of claim 2, wherein the sensorfor determining the thermal buildup in the electric cord and vehicleconnector assembly comprises a thermistor for measuring the temperatureproximate to the spool.
 5. The vehicle charging system of claim 2,wherein the sensor for determining the thermal buildup in the electriccord and vehicle connector assembly comprises a digital temperaturesensor for measuring the temperature proximate to the spool.
 6. Thevehicle charging of claim 1 further comprising a detection conductor inthe cord, the detection conductor being operatively connected at one endto the processor, and at the other end to a resistor in the vehicleconnector assembly.